Xampling: Signal Acquisition and Processing in Union of Subspaces

We introduce Xampling, a unified framework for signal acquisition and processing of signals in a union of subspaces. The main functions of this framework are two. Analog compression that narrows down the input bandwidth prior to sampling with commercial devices. A nonlinear algorithm then detects the input subspace prior to conventional signal processing. A representative union model of spectrally-sparse signals serves as a test-case to study these Xampling functions. We adopt three metrics for the choice of analog compression: robustness to model mismatch, required hardware accuracy and software complexities. We conduct a comprehensive comparison between two sub-Nyquist acquisition strategies for spectrally-sparse signals, the random demodulator and the modulated wideband converter (MWC), in terms of these metrics and draw operative conclusions regarding the choice of analog compression. We then address lowrate signal processing and develop an algorithm for that purpose that enables convenient signal processing at sub-Nyquist rates from samples obtained by the MWC. We conclude by showing that a variety of other sampling approaches for different union classes fit nicely into our framework.Comment: 16 pages, 9 figures, submitted to IEEE for possible publicatio

Coercive sexual practices and gender-based violence on a university campus

When a 22-year-old University of the Western Cape (UWC) female student was stabbed to death by her boyfriend (another student) in her room in the university residence on 25 August 2008, the entire campus was left reeling. Bringing the stark reality of gender-based violence (GBV) so close to home, the tragedy was a powerful reminder of the limits of more than a decade of legislative change, concerted activism, education, consciousness-raising and knowledge production aimed at challenging gender-based power inequalities. This article reflects on the relationships between violence, coercion and heterosexuality on a specific campus by drawing on data generated by a qualitative study at UWC that explored student constructions of heterosexual relationships in the light of national imperatives around HIV/AIDS and GBV. Involving 20 focus groups with male and female students over the course of 2008 and 2009, the study revealed that unequal and coercive practices are common in heterosexual relationships on this campus. The study underlined the necessity of understanding these relationships as produced through power inequalities inherent in normative gender roles, and also drew attention to ways in which gender power inequalities intersect in complex and sometimes contradictory ways with other forms of inequality on campus – in particular, class, age and geographical origin. While both men and women students appeared to experience pressure (linked to peer acceptance and material gain) to engage in (hetero)sexual relationships, it seems that first-year female students from poor, rural backgrounds are particularly vulnerable to the transactional and unequal relationships associated with coercive and sometimes even violent sexual practices. Alcohol and substance abuse also appear to be linked to unsafe and abusive sexual practices, and again it is young female students new to campus life who are most vulnerable. This article draws on the data from this larger study to explore experiences and understandings of the most vulnerable – young female students – in unpacking connections between (hetero)sexuality and violent and coercive sex in an educational institution.International Bibliography of Social Science

‘We do not cook, we only assist them’

This article discusses how the gendering of activity by boys coincides with, contests or recreates constructions of hegemonic masculinity in the context of South Africa. The study used a qualitative methodology including a series of three focus groups with 14–16 year-old boys across six different schools in the Western Cape, South Africa. A discursive analysis in which particular attention was paid to how participants construct their masculinity in relation to what they may or may not do as boys/men was conducted. The findings foreground how articulations of masculinity by boys are characterised by efforts to gender activity in the process of, amongst other things, counter blushing—meaning not to be regarded as girl-like or a moffie, or other derogatory notions that do not fit with hegemonic masculinity in a particular context. However, resistances and alternative views on what boys/men can and cannot do also emerged, highlighting the contested nature of current constructions of masculinity among young people in South Africa

Quantum Detection with Unknown States

We address the problem of distinguishing among a finite collection of quantum states, when the states are not entirely known. For completely specified states, necessary and sufficient conditions on a quantum measurement minimizing the probability of a detection error have been derived. In this work, we assume that each of the states in our collection is a mixture of a known state and an unknown state. We investigate two criteria for optimality. The first is minimization of the worst-case probability of a detection error. For the second we assume a probability distribution on the unknown states, and minimize of the expected probability of a detection error. We find that under both criteria, the optimal detectors are equivalent to the optimal detectors of an ``effective ensemble''. In the worst-case, the effective ensemble is comprised of the known states with altered prior probabilities, and in the average case it is made up of altered states with the original prior probabilities.Comment: Refereed version. Improved numerical examples and figures. A few typos fixe

Efficient Benchmarking (of Language Models)

The increasing versatility of language models LMs has given rise to a new class of benchmarks that comprehensively assess a broad range of capabilities. Such benchmarks are associated with massive computational costs reaching thousands of GPU hours per model. However the efficiency aspect of these evaluation efforts had raised little discussion in the literature. In this work we present the problem of Efficient Benchmarking namely intelligently reducing the computation costs of LM evaluation without compromising reliability. Using the HELM benchmark as a test case we investigate how different benchmark design choices affect the computation-reliability tradeoff. We propose to evaluate the reliability of such decisions by using a new measure Decision Impact on Reliability DIoR for short. We find for example that the current leader on HELM may change by merely removing a low-ranked model from the benchmark and observe that a handful of examples suffice to obtain the correct benchmark ranking. Conversely a slightly different choice of HELM scenarios varies ranking widely. Based on our findings we outline a set of concrete recommendations for more efficient benchmark design and utilization practices leading to dramatic cost savings with minimal loss of benchmark reliability often reducing computation by x100 or more

On the use of dexamethasone-loaded liposomes to induce the osteogenic differentiation of human mesenchymal stem cells

Article first published online: 7 Oct. 2013Stem cells have received considerable attention by the scientific community because of their potential for tissue engineering and regenerative medicine. The most frequently used method to promote their differentiation is supplementation of the in vitro culture medium with growth/differentiation factors (GDFs). The limitations of that strategy caused by the short half-life of GDFs limit its efficacy in vivo and consequently its clinical use. Thus, the development of new concepts that enable the bioactivity and bioavailability of GDFs to be protected, both in vitro and in vivo, is very relevant. Nanoparticle-based drug delivery systems can be injected, protect the GDFs and enable spatiotemporal release kinetics to be controlled. Liposomes are well-established nanodelivery devices presenting significant advantages, viz. a high load-carrying capacity, relative safety and easy production, and a versatile nature in terms of possible formulations and surface functionalization. The main objective of the present study was to optimize the formulation of liposomes to encapsulate dexamethasone (Dex). Our results showed that the optimized Dex-loaded liposomes do not have any cytotoxic effect on human bone marrow-derived mesenchymal stem cells (hBMSCs). More importantly, they were able to promote an earlier induction of differentiation of hBMSCs into the osteogenic lineage, as demonstrated by the expression of osteoblastic markers, both phenotypically and genotypically. We concluded that Dex-loaded liposomes represent a viable nanoparticle strategy with enhanced safety and efficacy for tissue engineering and regenerative medicine.The authors thank the Portuguese Foundation for Science and Technology for a PhD grant (No. SFRH/BD/62465/2009, to N. S. Monteiro). This work was partly supported by the FIND and BIND Project (No. NMP4-SL-2009-229292) and the OsteoGraphy Project (No. PTDC/EME-MFE/2008)

Fine-Scale Temporal Dynamics of a Fragmented Lotic Microbial Ecosystem

Microbial ecosystems are often assumed to be relatively stable over short periods of time, but this assumption is seldom tested. An urban stream influenced by both flow and varying levels of anthropogenic influences is expected to have high temporal variability in microbial composition, and short-term ecological instability. Thus, we analyzed the bacterioplankton composition of a weir-fragmented urban stream using Automated rRNA Intergenic Spacer Analysis (ARISA). A total of 46 sequential samples were collected in July 2009 for 7 days, every 7 hours, from both the up-stream side of the weir (stream water) and the downstream side of the weir (estuarine) water. Bray-Curtis similarity based analysis showed a clear division between upstream and downstream communities. A sudden pH drop induced change in both communities, but composition stability partially recovered within less than a day. Thus, our results show that microbial ecosystems can change rapidly, but re-establish a new equilibrium relatively quickly